Planktic foraminifera as paleoceangraphic indicators: Production, preservation, and reconstruction of upwelling intensity, implications from late quarternary South Atlantic sediments.

Abstract

To explain the lowered atmospheric CO2 content of glacial times, Iysocline reconstructions play an important role as they are useful tools to determine variations in the depth gradient of understaturation in the deep ocean (Berger 1977; Broecker and Clark, 1999). When investigating calcium carbonate dissolution thoughout the different hydrologic and ecologic settings of the South Atlantic, a reliable proxy is needed. As shown in manuscript 2 and 3, conventional calcium carbonate dissolution proxies are biased by increased surface productivity and could mimic calcium carbonate dissolution in high productive upwelling regions. So far, only a time-consuming multiproxy approach consisting of several conventional dissolution proxies indicates the alteration of a sediment sampie with certainty. However, in high-productivity regions even a multi-proxy approach could hardly determine whether the sediment reflects its original (unaltered) composition or not (manuscript 1). To overcome this problem, all further investigations were carried out with the Globigerina bulloides dissolution index (BOX'), an independent calcium carbonate dissolution proxy, that concentrates on the ultrastructure of the planktic foraminifera Globigerina bu/loides. The degree of dissolution is reflected by five dissolution stages determined from test morphology.